1. Field of the Invention
The present invention relates to a collision preventing device for a measuring apparatus and a measuring apparatus having a collision preventing unit. More particularly, the present invention relates to a collision preventing device for a measuring apparatus and a measuring apparatus having a collision preventing unit, the measuring apparatus measuring dimensions and the like of a work while relatively moving the work and a non-contact probe by a driving system.
2. Description of the Related Art
As a measuring apparatus using a non-contact probe, a non-contact view measuring CMM (Coordinate Measuring Machine) is known. The non-contact view measuring CMM is capable of measuring the dimensions and the like of a work on the basis of an image fetched by a non-contact probe while moving the work or the non-contact probe in an X-axis direction, a Y-axis direction, and a Z-axis direction that are mutually perpendicular to each other.
In FIG. 13, a non-contact view measuring CMM 1 is provided with a measuring table 11 and a bridge-type frame 12. The bridge-type is capable of moving on the measuring table 11 in the Y-axis direction. A guide rail 13 is attached to one side of the measuring table 11, and one leg 121 of the bridge-type frame 12 moves while sliding in the Y-axis direction along this guide rail 13.
Here, the relative displacement of the bridge-type frame 12 and the guide rail 13 is measured by a displacement detecting unit including a scale 14 disposed on the guide rail 13 and a detector (not shown) disposed on the leg 121. It should be noted that an air bearing or the like is provided on the underside of the other leg 122 of the bridge-type frame 12, whereby the leg 122 is slidably supported on the measuring table 11.
Meanwhile, an X-axis slider 15 is disposed on a bridge 123 in such a manner as to be slidable in the X-axis direction, and the relative displacement of the bridge 123 and the X-axis slider 15 is measured by a displacement detecting unit similar to that for the Y-axis direction. The bridge 123 bridges between the legs 121 and 122 of the bridge-type frame 12. Further, a Z-axis supporting member 16 is disposed on the X-axis slider 15, and this Z-axis supporting member 16 is provided with a Z-axis spindle 17 which is slidable in the Z-axial direction. A non-contact probe 18 is attached to the Z-axis spindle 17, and this non-contact probe 18 includes a CCD camera 181 and an objective 182 attached to the CCD camera 181.
The non-contact probe 18 is movable in the X-, Y-, and Z-axis directions by a driving system (not shown) provided in the non-contact view measuring CMM 1. Although not shown, the driving system has an X-axis driving system, a Y-axis driving system, and a Z-axis driving system for moving the non-contact probe to in the X-, Y-, and Z-axis directions. For example, the driving system is adapted to be operated manually or by inputting coordinates to a computer (not shown) connected to the driving system.
The measurement, the non-contact probe 18 is first moved in the X-, Y-, and Z-axis directions along the work by the driving system. Next, in a state in which the non-contact probe 18 is positioned at a desired position, an image of the work is fetched by the CCD camera 181. The dimensions and the like of the work are then determined from this image.
The non-contact probe 18 of the above-described non-contact view measuring CMM 1 is used at a position proximate to the work. At the time of measurement, in particular, the non-contact probe 18 is moved in a three-dimensional direction, but there are cases where the non-contact probe 18 is made to collide against the work due to the carelessness of an operator or such as an error in the input setting of coordinates to the computer. In addition, in the case of an apparatus having a number of devices, such as a combination measuring apparatus, a mechanism is often adopted in which the devices are stored except when necessary, and a device, when necessary, is moved to a normal position so as to be used. In such a case as well, unless the distance between the device and the work is proper, there is a possibility of causing the device to collide against the work.
Since the above-described non-contact probe 18, the devices, and the line are not provided with the collision detecting capability in themselves, even if the non-contact probe 18, for instance, collides against the work, the driving force of the driving system continues to be applied to the non-contact probe 18. The driving system stops only when an overload has been applied to the driving system, or an overcurrent has occurred, or an error signal such as a servo tracking error in the driving system has been issued from the driving system. For this reason, there is a problem in that large damage may be possibly imparted to the main body, the driving system, and the non-contact probe 18 of the non-contact view measuring CMM 1 or the work.